Airway infection begins the cascade of inflammation and pathology that destroys the lungs of people with cystic fibrosis (CF). Therefore, early intervention aimed at correcting the initial host defense defects could dramatically improve the course of CF lung disease. We discovered that in newborn CF pigs, the ASL was more acidic, and bacterial killing was impaired. Reducing ASL pH in non-CF pigs inhibited bacterial killing, and raising ASL pH in CF pigs rescued bacterial killing. These results directly link the loss of CFTR, an anion channel that facilitates HCO3 transport, to an initial host defense defect. We studied children with CF and found that like newborn CF pigs, they had reduced ASL pH. However in adults, ASL pH did not differ between CF and non-CF, suggesting that the inflammation associated with chronic disease may have elevated the pH. In preliminary work, we found that cultured porcine CF airway epithelia lack cAMP stimulated HCOs transport, but freshly isolated CF airway epithelia retain some HCO3' secretion. The overall goal of this project is to understand the mechanisms that control ASL pH in CF airways and to learn how pH influences bacterial killing by ASL antimicrobial peptides and proteins. To achieve our goals, we will use a novel porcine model of CF that will allow us to investigate the airways immediately after birth and then as airway disease progresses. Aim 1. Does respiratory virus infection and/or bacteria-induced inflammation change ASL pH and bacterial killing? Infection with common respiratory viruses predisposes infants to airway bacterial infections. We hypothesize that loss of CFTR hinders a normal compensatory response that enhances anti-bacterial activity and thereby increases the risk to CF airways of bacterial infection. Conversely, we hypothesize that the onset of inflammation with early bacterial infections triggers enhanced ASL alkalinization as well as antimicrobial peptide production. Discovering the mechanistic bases by which inflammation enhances bacterial killing in CF will suggest interventions to augment antibacterial innate immunity. Aim 2: How is HCO3 secretion regulated in CF airway epithelia? In the absence of CFTR, CF airway epithelia can still support some HCO3 secretion. We will identify the channels and transporters that control HCO3 secretion, and we will learn how inflammation modifies their expression. The results will suggest potential means to raise ASL pH in CF airways and enhance bacterial killing prior to the onset of disease. Aim 3: How does pH affect bacterial killing by ASL antimicrobial peptides? Preliminary data show that reduced pH inhibits bacterial killing by some antimicrobial peptides. Our working hypothesis is that pH affects charge-dependent binding of antimicrobial peptides to the bacterial cell wall, and hence killing. We will also identify bacterial genes that interfere with normal pH-sensitive antimicrobial peptide killing. Understanding the mechanisms involved in these processes will aid understanding of why some bacteria are resistant to ASL antimicrobials.